You still can't tickle yourself, even if you swap bodies with another person

You wouldn't believe the amount of ink spilled by neuroscientists and psychologists attempting to explain the simple fact that we can't tickle ourselves. A popular, long-standing theory posits that the self-tickle failure occurs because of the way that the brain cancels out sensations caused by its own movements. To do this, so the theory states, the brain uses the motor command underlying a given action to make a prediction of the likely sensory consequences of that action. When incoming sensory information matches the prediction, it's recognised as self-generated and cancelled.

If this explanation is true, then any situations that confuse the brain's ability to predict the sensory consequences of its own actions should scupper the sensory cancellation process, thereby making self-tickling a possibility. George Van Doorn and his colleagues have put this principle to the test in dramatic fashion. They measured the potential for self-tickling in 23 participants who underwent a body-swap illusion (open access article here).

During the body-swap illusion, the participants said they felt the sensation of the foam, not where their real hand was located, but at the position of the experimenter's hand. Given the illusion, they perceived this to be their own hand, even though it looked like someone else's. Crucially, even in this strange situation, the participants were still unable to tickle themselves if they were the ones moving the rod (they felt the foam, but it didn't tickle). They felt much more of tickling sensation when it was the experimenter who moved the rod.